Duterte cut short his trip to Russia in response to the attack. His home city of Davao, where he served as mayor before winning the presidency, is in the region now under martial law.

Duterte has faced international criticism for his violent approach to tackling the illegal drug trade. A few days before the attack, he hinted that he might use martial law to deal with both terrorism and drug trafficking.

"If I declare martial law in Mindanao, I will solve all that ails the island. ... There will be no guarantee that it will not last until the end of my term," Duterte said.